The present invention relates generally to the art of bonding polycarbonate to metal, and more particularly to the art of bonding polycarbonate to stainless steel at relatively low temperatures.
Aircraft windshields are commonly laminated articles comprising an exposed polycarbonate ply, and also comprising stainless steel bearing strips adhered to the polycarbonate along the aft edge of the windshield. It has been customary to bond both inboard and outboard metal retainers to polycarbonate using silicone adhesives, chosen for their resistance to adverse environments and their flexibility over a wide range of temperatures. However, these silicones are inherently relatively weak materials, and do not have sufficient strength to withstand the force generated by impact. For example, upon bird impact, the inboard metal bearing strip may debond, exposing the polycarbonate and providing a potential for damage inside the cockpit.
Since the inboard side of an aircraft windshield is not exposed to as severe an environment as is the outboard, a silicone adhesive may be advantageously replaced on the inboard side with a stronger adhesive so long as the stronger adhesive meets the requirements of compatibility with polycarbonate, high peel and tensile strength, thermal stability and solvent resistance. In addition, for process feasibility, the adhesive should have a reasonable pot life but still be curable at moderate temperatures, and should be relatively safe to process. A two component system may be preferred.